The present invention relates generally to the conveying field and, more particularly, to an improved apparatus that effectively and efficiently scrapes carry back material from a conveyor belt during relative forward movement of the belt.
Endless belt conveyors are well known in the art. The belt is stretched in an endless path between two main support rolls, and is usually driven by the roll near the discharge end of the conveyor. The belt may be formed of coated or impregnated plastic fabric. Idler roller assemblies guide and support the belt throughout its length.
Where bulk materials are being conveyed, the idler assemblies may form a trough of the carrying side of the belt. More specifically, at each support location three idler rollers may be utilized. The middle roller is level and the side rollers are directed upwardly and inclined at an angle of, for example, 25.degree.. In this manner, the belt is provided with a substantially U-shaped cross section to better maintain the bulk material on the belt during conveying. In addition, other idler assemblies engage the bottom face of the belt as it travels along an underlying return run in the reverse direction. These idler assemblies also serve to maintain proper alignment of the belt during conveyor operation.
Due to outstanding reliability and efficiency, belt conveyors have been found to be particularly useful in conveying large quantities of bulk material from place to place. Thus, belt conveyors have a wide range of applications. For example, a series of belt conveyors may be utilized to convey coal from a shuttle car, scoop or tractor trailer dumping station in an underground mine to a storage bin or coal pile at the surface.
A primary concern in underground mining relates to the suppression of coal dust. This is because inhalation of coal dust over a long period of time may lead to the serious health affliction known as black lung. Additionally, it should be recognized that coal dust is explosive and when present in certain quantities in air can be ignited by a spark. Thus, in order to improve safety, dust allaying equipment is provided to spray foam or water on the aggregate coal where coal is put on a conveyor system as well as where coal is transferred from one conveyor to another.
The foam bubbles or water droplets mix with the fine particles of coal and other dust in the mine to create a mud or slurry that tends to stick or cake to the conveyor belt. Upon reaching the discharge end of the conveyor, the endless belt travels around the end roll of the conveyor to the return run. The aggregate coal is discharged from the belt at this time, but the wet, fine particles and dust often remain stuck to the belt. This "carry back material" may build up on the idler assembly rollers that support the material carrying face of the belt along the return run. Often, the build-up of material on these idlers is uneven resulting in the application of uneven guiding pressure to the belt. Eventually this condition may lead to belt misalignment that adversely affects the efficient operation of the conveyor. Where, in fact this condition becomes severe, the belt could become damaged resulting in the costly closing down of the conveyor for repairs.
It should also be appreciated that the carry-back material has a gritty, abrasive character. Thus, when disposed between an idler and the belt, overall wear of the belt is greatly increased. This, of course, results in reduced belt surface life.
As a further consideration, carry back material stuck to the conveyor belt adds weight to the belt. On relatively long endless belt conveyors this added weight can lead to a substantial increase in the power requirements for operation. Further, it reduces the capacity of the conveyor to convey aggregate coal thereby reducing operating efficiency.
Recognizing these shortcomings, several systems have been developed for removing carry back material from a conveyor belt during conveyor operation. One such belt scraper is manufactured by Richwood Industries, Inc. and sold under the trademark COMBI-T. This system utilizes dual scraper blades in combination with a center roller. While this system effectively cleans carry back material from a conveyor belt under numerous operating conditions, it is not as effective in cleaning as desired where the carry back material is relatively heavy.
More specifically, both the upstream and downstream scraper blades are oriented perpendicular to the surface of the conveyor belt with scraping pressure applied equally on each blade. Where the carry back material is heavy, the upstream blade removes only a portion of the carry back material and actually tends to grind the remainder of the carry back material into the surface of the belt including the pores. Disadvantageously, this results in excessive wear of the belt coating and fabric that could preferably be avoided.
It should also be recognized that the COMBI-T scraper fails to provide any the air shocks that apply scraping pressure to the scraper blades. In the adverse operating conditions existing in an underground mine, it is not unusual to suffer a loss of air pressure through hose or, air cylinder failure. Disadvantageously, with the COMBI-T scraper system, such a loss of pressure would mean that the conveyor belt would have to be shut down until repairs could be made to the air system. Alternatively, continued operation of the conveyor belt would be possible, but there would be no effective, operational scraper system. As a result, continued operation is only possible while suffering all the disadvantages noted above with respect to carry back material build-up on a conveyor belt.